In the processing of uranium hexafluoride into fuel for nuclear reactors, uranium hexafluoride gas is dissolved in water to form UO.sub.2 F.sub.2. Ammonium diuranate (ADU) is then precipitated from the solution by the addition of the ammonium hydroxide. The ADU precipitate is separated from the solution and is calcined to produce UO.sub.2, which is pressed and sintered into pellets for use in reactors.
If the ADU precipitate is too coarse, the resulting pellets of UO.sub.2 will not be dense enough to perform satisfactorily in a reactor. On the other hand, if the particle size of the ADU precipitate is too fine, the resulting UO.sub.2 pellets may crumble and fall apart. It has been found that the ideal particle size is achieved when the surface area of the ADU particles is about 10 to about 20 M.sup.2 /g. Until now, it has been difficult to control the process variables during the precipitation of the ADU to consistently and repeatedly achieve a particle size within the desired range. Since, in the UO.sub.2 -NH.sub.4 OH-H.sub.2 O system, particle growth is favored over nucleation, the ADU particles formed are normally too large for use in making UO.sub.2 pellets.